{"id":"bafb0f6c-a4fa-4167-866b-b09dd5f4cda6","arxiv_id":"1909.00592","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Simulated e+e- -> ttbar + jet events at 500 GeV and 3 TeV show future lepton colliders could limit top-quark SMEFT Wilson coefficients down to 10^-3 to 10^-4 at 95% CL.","lead":"This paper uses simulated data to estimate how well future electron-positron colliders could measure tiny deviations in top quark couplings. It finds that producing a top quark pair together with an extra jet could constrain new-physics coefficients to about 10^-3 to 10^-4.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The claimed 10^-4 reach is extrapolated from a BDT trained at c=0.1, where signal is ~70x background; no check shows this MVA remains sensitive at c~2e-4.","rationale":"The reader's CONDITIONAL verdict is appropriate. The generic Monte Carlo/LO concern is real, but the more sharply load-bearing issue for the central 10^-4 claim is the use of a multivariate classifier trained at c=0.1, where the EFT signal is 70 times the SM ttbar+jet background, to derive limits at c~2e-4, where the signal is a small perturbation. The manuscript does not state whether the BDT is retrained or the cut re-optimized per coefficient value, nor does it validate the linearity of the signal efficiency across three orders of magnitude in the Wilson coefficient. This is an internal statistical-modeling gap, not an attack on the authors; it is checkable with the same simulation setup by retraining or by using a cut-based analysis as a cross-check. I therefore keep the reader's CONDITIONAL verdict rather than moving to ACCEPT, and I identify a more precise condition than the general MC-chain concern.","tokens_in":18770,"tokens_out":25248,"duration_ms":269303,"concrete_test":"Retrain the BDT with signal samples generated or reweighted to c=1e-4 (or using only the linear SMEFT interference term) and recompute the 95% CL intervals at 500 GeV for 500 fb^-1 and 4 ab^-1; alternatively, repeat the limit extraction with a simple cut-and-count analysis on the preselected cross sections of Table 1, without the BDT. If the resulting cbar_uW and cbar_uB intervals widen by more than about a factor of 2 relative to Table 2, the claimed 10^-4 reach is an artifact of extrapolating the c=0.1-trained MVA.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Section 3 trains the gradient BDT on benchmark signals with c=0.1 (e.g., Fig. 5), and Table 1 reports post-MVA signal cross sections at c_uB=c_uW=0.1 of about 247.5 fb at 500 GeV versus 3.8 fb total background. The central claim, however, is sensitivity at c~1e-4 (Table 2 gives cbar_uW upper edge 2e-4 at 4 ab^-1), where the EFT signal is a small perturbation on the SM ttbar+jet background and the S/B ratio is very different from the training point. The paper does not document whether the BDT is retrained for each coefficient value or how the optimal BDT cut is re-optimized at small couplings. If a fixed c=0.1-trained cut is applied, the small-c signal efficiency, and hence the 95% CL intervals, are not established. This is load-bearing because the claimed reach is a three-order-of-magnitude extrapolation of the MVA performance.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper presents a Monte Carlo projection of the sensitivity of e+e- -> t tbar + jet production at sqrt(s) = 500 GeV and 3 TeV to six CP-conserving dimension-six SMEFT operators in the SILH basis. The analysis uses MadGraph5 leading-order matrix elements with MLM merging, PYTHIA for showering and hadronization, Delphes with an ILD-like detector simulation, and a gradient-boosted decision tree in the dileptonic t tbar final state. Expected 95% CL limits are reported for cbar_uW, cbar_uB, cbar_uG, cbar_Hu, cbar_HQ, and cbar'_HQ at two energies and several integrated luminosities, with the strongest claims being sensitivity to cbar_uW and cbar_uB at the 10^-3 to 10^-4 level. The paper argues that adding the t tbar + jet process to t tbar improves the reach of future e+e- colliders to top-quark electroweak couplings.","tokens_in":19027,"tokens_out":9373,"duration_ms":94704,"significance":"If the projected limits are reliable, the paper would provide a useful cross-check of SMEFT top-quark coupling constraints at future lepton colliders, especially for the electroweak dipole operators O_uW and O_uB. The simulation chain is realistic in several respects: it uses a full detector response via Delphes/ILD, includes the dominant backgrounds, applies MLM merging, and considers two center-of-mass energies with different luminosity scenarios. However, the central quantitative claims rest on an incompletely specified statistical procedure and on a multivariate classifier trained at large Wilson coefficients, so the numerical limits should be treated with caution. The paper does not provide machine-checked derivations or reproducible code; its value is as an indicative phenomenological projection rather than a definitive sensitivity statement.","major_comments":[{"comment":"The paper never specifies the statistical procedure used to convert simulated event counts into the quoted 95% CL intervals. No likelihood, chi-square, Bayesian, CL_s, or profile-likelihood construction is given, and it is unclear whether the contours in Figs. 6 and 7 are simultaneous two-dimensional limits or one-dimensional projections, or how the 'marginalised limits over all contributing operators' mentioned in the text are computed. Because the limits are the central quantitative result, this omission prevents the reader from reproducing or interpreting the numbers.","section":"Section 4, Table 2"},{"comment":"The gradient BDT is trained and its optimum cut is chosen on benchmark signals with Wilson coefficients set to 0.1 (e.g., cbar_uB = cbar_uW = 0.1), where the post-MVA signal is 247.5 fb against 3.6 fb of SM t tbar + jet background at 500 GeV. The claimed reach in Table 2 extends to c ~ 2e-4, where the full SMEFT signal sample is nearly indistinguishable from the SM t tbar + jet background by construction, and where c = 0.1 is outside the global-fit interval of Eq. (5) for cbar_uW. The paper does not document whether the BDT is retrained for each coefficient value or whether the cut is re-optimized as a function of c; if a fixed c = 0.1 benchmark is applied, the signal efficiency at small c is not established. This is load-bearing because the reach claim is an extrapolation over three orders of magnitude in the Wilson coefficient.","section":"Section 3, Figs. 4-5 and Table 1"},{"comment":"The projected limits rely on leading-order matrix elements, as stated in Section 3, and on an ad hoc 10% systematic uncertainty on background rates and signal efficiency in Section 4. There is no scale variation, no xqcut/qcut variation, no estimate of NLO or electroweak corrections, and no derivation of the 10% number. At sqrt(s) = 3 TeV, where limits near 10^-3 are claimed, even moderate corrections to the signal acceptance or background normalization can shift the contours by an amount comparable to the quoted reach. The dependence of the limits on these choices should be quantified, for example by varying the merging scales and by applying NLO k-factors or scale-uncertainty bands.","section":"Sections 3 and 4"},{"comment":"The claim that adding e+e- -> t tbar + jet to e+e- -> t tbar improves the sensitivity is not demonstrated by the presented analysis. The paper compares its t tbar + jet limits with the t tbar -only results of Ref. [75] only in words, stating that the results are comparable and that a combination would improve, but it does not perform a t tbar -only analysis with the same generator, detector simulation, and statistical treatment. The improvement claim therefore lacks a direct quantitative basis.","section":"Abstract and Section 4"},{"comment":"The abstract's statement that the Wilson coefficients 'could be probed down to 10^-4' overstates the tabulated results. Table 2 gives cbar_uW in [-0.011, 0.0002] and cbar_uB in [-0.017, 0.0003] at sqrt(s) = 500 GeV with 4 ab^-1, so the best upper edges are 2e-4 and 3e-4, while at 500 fb^-1 the corresponding edges are 6e-4 and 9e-4. Unless the 10^-4 quote is intended only as an order-of-magnitude statement, it should be made precise and consistent with the table.","section":"Abstract and Table 2"}],"minor_comments":[{"comment":"The acronym 'CPEC' appears to be a typo for 'CEPC' (Circular Electron Positron Collider); please correct it.","section":"Section 1"},{"comment":"The caption should state explicitly that the quoted 'Signal' cross sections include the full SMEFT cross section, i.e., the SM piece plus the EFT contribution, not only the EFT-induced excess; this is essential for interpreting the small-c extrapolation.","section":"Table 1 caption"},{"comment":"The sentence 'the results from this analysis derives comparable bounds' should be rephrased for grammar; more substantively, the comparison with Ref. [75] should state what luminosity, polarization, and statistical procedure are being assumed for the quoted t tbar -only limits.","section":"Section 4"},{"comment":"The sentence 'Some plots are magnified for better clarity' does not identify which panels are magnified; please indicate the magnified panels or remove the statement.","section":"Figure 7 caption"},{"comment":"The requirement of 'exactly two same flavour opposite sign isolated charged leptons' should clarify whether e±mu∓ events are excluded; the dileptonic t tbar decay yields e+e-, mu+mu-, and e±mu∓ final states, so the same-flavour requirement removes one of the three categories and this choice should be justified.","section":"Section 3"}],"recommendation":"major_revision","confidential_remarks":"The paper is a plausible phenomenological projection, but the missing statistical definition and the MVA extrapolation from c = 0.1 to c ~ 1e-4 are serious gaps that need to be addressed before the quantitative limits can be trusted. I would not reject outright because the analysis can in principle be fixed by documenting or rerunning with a proper likelihood and by validating the classifier at small coefficients. The novelty is moderate: the t tbar + jet channel adds information beyond t tbar alone, but the paper does not quantify this against a consistent t tbar baseline, and the comparison with existing global fits should be updated. The benchmark training at c = 0.1 for cbar_uW is outside the global-fit interval quoted in Eq. (5), which strengthens the need for a small-c validation."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take: this is a competent but incomplete sensitivity study. The physics is plausible and the topic is timely, but the paper doesn't document how the limits are computed and the MVA training point raises a real question about the extrapolation to small couplings. With those gaps fixed, it would be a useful reference for future lepton collider planning.\n\nWhat's new: the e+e- -> ttbar+jet process with SMEFT and a realistic ILD-like detector simulation hasn't been done in the cited literature. The operator list and tools are standard, but the extension to an extra jet adds information on the energy dependence of the dipole operators. The background list is reasonably complete and the MLM merging is described.\n\nWhere it gets soft: first, there is no statistical procedure anywhere. Section 4 just gives 95% CL limits. Poisson counting? chi-square? Bayesian? The reader can't reproduce the numbers. That's a basic omission. Second, the whole chain is LO with an ad hoc 10% systematic on background rates and signal efficiency. At 3 TeV the background rates are tiny, so a factor of two change in a background could shift the limits noticeably. Third, the BDT is trained on signal benchmarks with c=0.1, where Table 1 shows signal is tens to hundreds of times the background. The claimed limits reach c ~ 2e-4, where the EFT is a small perturbation. The text doesn't say whether the BDT is retrained for each coefficient value or how the cut is re-optimized. If a fixed high-c BDT is applied at small c, the signal efficiency and hence the limits are not established. That's the biggest technical concern, and it's load-bearing for the headline 10^-4 reach. Finally, the abstract and introduction say the ttbar+jet process 'improves' on ttbar alone, but no quantitative comparison is given. Ref [75] reportedly reaches ~1e-4 on the same operators with ttbar; the paper says 'comparable bounds' in section 4, so the improvement claim is not substantiated.\n\nAll that said, this is not a throwaway. The process does have a different energy reach and the results are plausible within the stated approximations. Who should read it: people doing global SMEFT fits for CLIC/ILC and anyone comparing measurements at different energies. It deserves a serious referee, but the revision needs to state the statistical method, address the MVA retraining question, and soften the improvement claim unless it can be shown.\n\nRecommendation: send to peer review, but with a strong request to address the missing methodology before acceptance.","headline":"A useful but methodologically under-documented SMEFT sensitivity study for e+e- -> ttbar+jet; the limits are plausible but the missing statistical procedure and the MVA extrapolation from c=0.1 to c~1e-4 need to be addressed before the numbers can be trusted.","tokens_in":19494,"tokens_out":2694,"would_cite":false,"duration_ms":190836,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Top-quark pair production with an associated jet at future electron-positron colliders can constrain top-quark new-physics operator coefficients down to 10^-4.","keywords":["top quark","top quark pair production with a jet","SMEFT","SILH basis","Wilson coefficients","future lepton colliders","dileptonic final state","multivariate analysis"],"falsifier":"Recompute the analysis with next-to-leading-order QCD corrections to $e^-e^+ \\to t\\bar{t}+\\text{jet}$ and compare the predicted dileptonic cross sections and BDT output distributions at 500 GeV and 3 TeV with the leading-order predictions. If the shifts exceed the assumed 10% uncertainty band, the projected $10^{-4}$ limits would move correspondingly, and a measurement at a future collider that deviated by more than that band would directly invalidate the bounds.","tokens_in":18602,"feed_emoji":"⚛️","tokens_out":11509,"duration_ms":105928,"temperature":0.7,"pith_summary":"This paper argues that $e^-e^+ \\to t\\bar{t}+\\text{jet}$ at future electron-positron colliders can measure the effective field theory of top-quark couplings with greater sensitivity than $t\\bar{t}$ production alone. Working in the SILH operator basis, the authors study the dimension-six operators that modify the $t\\bar{t}\\gamma$, $t\\bar{t}Z$, and $t\\bar{t}g$ vertices and simulate the dileptonic final state at center-of-mass energies of 500 GeV and 3 TeV, including detector response and the main backgrounds. They find that the momentum-dependent dipole operators $O_{uW}$ and $O_{uB}$ produce large energy-growing enhancements of the cross section, and they project 95% CL limits on normalized Wilson coefficients down to $10^{-3}$ at 3 TeV and $10^{-4}$ at 500 GeV in the most favorable scenarios. If these projections hold, future lepton colliders would be able to probe new physics coupled to the top quark at scales well above the collision energy.","feed_headline":"One extra jet could reveal top-quark new physics at the 10^-4 level","feed_subtitle":"Future e+e- colliders at 500 GeV or 3 TeV could pin top-photon and top-Z dipole couplings to 10^-4.","key_machinery":"The load-bearing object is the set of dimension-six, CP-conserving operators in the SILH basis that involve the top quark, especially the dipole operators $O_{uW}$ and $O_{uB}$, with normalized coefficients $\\bar{c}_i = c_i v^2/\\Lambda^2$. Their vertices grow with the momentum flowing through the virtual photon or $Z$, which is why the high-energy cross-section ratio rises by factors of 20-40. On the analysis side, the sensitivity comes from merging 0- and 1-parton matrix elements, simulating an ILD-like detector response, reconstructing jets with the anti-$k_T$ algorithm, requiring two opposite-sign leptons and two $b$-tagged jets, and feeding kinematic variables such as $H_T$, the $b$-jet invariant mass, and lepton and jet pseudorapidities into a gradient-boosted decision tree.","core_discovery":"The central claim is that adding a resolved jet to top-quark pair production turns $e^-e^+ \\to t\\bar{t}+\\text{jet}$ into a sensitive probe of the electroweak dipole operators $O_{uW}$ and $O_{uB}$, because the virtual photon and $Z$ boson can carry momentum up to the full center-of-mass energy. At 3 TeV with normalized coefficients $\\bar{c}_{uW}=\\bar{c}_{uB}=0.03$, the merged $t\\bar{t}/t\\bar{t}+\\text{jet}$ cross section is enhanced by factors of roughly 20 and 40 respectively, while $O_{uG}$ at the same value adds only about a factor of two. The paper projects 95% CL bounds reaching the $10^{-3}$ level for $\\bar{c}_{uW}$ and $\\bar{c}_{uB}$ with 3 ab$^{-1}$ at 3 TeV and the $10^{-4}$ level at 500 GeV in the best scenarios, with the same limits translating to a new-physics scale $\\Lambda \\gtrsim 17$ TeV for $c_X=1$ and a bound $M \\gtrsim 7$ TeV in the strongly interacting Higgs regime $g_* = 4\\pi$. Operators $O_{HQ}$, $O'_{HQ}$, and $O_{Hu}$ have little effect on the rate and are constrained only weakly.","pith_inferences":["The energy-growing behavior suggests that a simultaneous fit to 500 GeV and 3 TeV data could separate $O_{uW}$ from $O_{uB}$ through their different scaling with $\\sqrt{s}$, a handle the paper does not explicitly exploit.","The $10^{-4}$ projection comes from one-sided intervals that extend to values near zero; adding next-to-leading-order QCD corrections and more realistic systematic uncertainties would test how stable that reach is.","Extending the same selection to the semileptonic $t\\bar{t}$ channel and to beam-polarization setups, which the paper mentions as possible improvements, could turn the projected limits into a more complete top-coupling fit."],"forward_implications":["Projected 95% CL bounds on $\\bar{c}_{uW}$ and $\\bar{c}_{uB}$ would improve on the current percent-level limits from $t\\bar{t}Z$ and $t\\bar{t}W$ measurements and on the global-fit ranges quoted in the paper.","The implied scales $\\Lambda \\gtrsim 17$ TeV (for $c_X=1$) and $M \\gtrsim 7$ TeV (strongly interacting Higgs, $g_*=4\\pi$) mean the process remains a discovery channel even if new particles are too heavy for direct production.","At 3 TeV with 3 ab$^{-1}$, the projected reach on $\\bar{c}_{uG}$ is about $|\\bar{c}_{uG}| \\lesssim 0.03$-$0.04$, which would tighten the current global-fit range for the gluon-dipole coefficient.","Operators that modify the top-quark coupling through four-quark or Higgs-current terms ($O_{HQ}$, $O'_{HQ}$, $O_{Hu}$) are barely constrained by this channel, so other observables are still needed for them."],"supporting_citations":[{"why":"Provides the $t\\bar{t}$-based projections for $\\bar{c}_{uW}$ and $\\bar{c}_{uB}$ that this analysis compares against and extends.","marker":"[75]"},{"why":"Supplies the global-fit prior constraints on the same Wilson coefficients quoted in Eq. (5).","marker":"[46]"},{"why":"Defines the SILH basis and the operator set underlying the effective Lagrangian.","marker":"[67]"},{"why":"Gives the strongly-interacting-Higgs estimate that converts coefficient limits into the new-physics mass scale $M$.","marker":"[74]"},{"why":"Generates the leading-order signal and background matrix elements used in the simulation.","marker":"[83]"},{"why":"Supplies the MLM matching prescription used to merge 0- and 1-parton samples.","marker":"[86]"},{"why":"Provides the fast detector simulation used to model the ILD-like response.","marker":"[90]"},{"why":"Supplies the b-tagging efficiencies and detector parameters used in the analysis.","marker":"[91]"},{"why":"Provides the anti-$k_T$ jet algorithm used for jet reconstruction.","marker":"[92]"}],"fun_headline_variants":["Top-quark EFT probed to 10^-4 via e+e- → ttbar + jet","Extra jet sharpens top EFT reach to 1e-4 at future colliders","Top-quark new physics via ttbar+jet: 95% CL to 10^-4","ttbar+jet at 500 GeV or 3 TeV pin top dipole couplings to 1e-4","Top EFT bounds from ttbar+jet reach 10^-4 at e+e- colliders"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The entire projection depends on the leading-order matrix-element simulation with parton-shower merging and an ILD-like detector response predicting the true signal and background rates and shapes at 500 GeV and 3 TeV, with only an ad hoc 10% systematic uncertainty covering missing higher-order and modeling effects.","fun_headline_variants_meta":{"raw":{"variants":["Top-quark EFT probed to 10^-4 via e+e- → ttbar + jet","Extra jet sharpens top EFT reach to 1e-4 at future colliders","Top-quark new physics via ttbar+jet: 95% CL to 10^-4","ttbar+jet at 500 GeV or 3 TeV pin top dipole couplings to 1e-4","Top EFT bounds from ttbar+jet reach 10^-4 at e+e- colliders"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001263,"raw_usage":{"total_tokens":5201,"prompt_tokens":1006,"completion_tokens":4195,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":622,"completion_tokens_details":{"reasoning_tokens":4067}},"tokens_in":622,"tokens_out":4195,"duration_ms":27582,"temperature":1.0,"reasoning_tokens":4067,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T05:42:46.342273+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Recompute the analysis with next-to-leading-order QCD corrections to $e^-e^+ \\to t\\bar{t}+\\text{jet}$ and compare the predicted dileptonic cross sections and BDT output distributions at 500 GeV and 3 TeV with the leading-order predictions. If the shifts exceed the assumed 10% uncertainty band, the projected $10^{-4}$ limits would move correspondingly, and a measurement at a future collider that deviated by more than that band would directly invalidate the bounds.","supporting_citations":[],"review_version":1}